1. Field of the Invention
The present invention generally relates to an optical device, such as an interferometer, for routing or demultiplexing data.
2. Background Information
Conventional wavelength division multiplexing (WDM) systems efficiently use bandwidth in existing fiber-optic telecommunication infrastructures. Such systems provide point-to-point optical transmission at high aggregate rates ( greater than 100 Gb/s) without compromising on high performance. Future requirements of digital communication networks indicate that increased data-rate capacity is critical to a service provider""s success in the market. Ultimately, all-optical networks will replace today""s optical/electrical networks that suffer from the bottlenecking effects of optical-to-electrical-to-optical conversions due to the limited capacity of electronic devices. Devices that can optically process data without converting it to an electronic format are essential to this network capacity evolution.
Several forecasts have predicted that there will be a tremendous growth in the sensor market. In contrast to the classical sensors based largely upon the measurement of electrical parameters such as variable resistance or capacitance, modern sensors make use of a variety of novel phenomena. More importantly, these sensors are directly suitable for digital control and also have a degree of smartness incorporated in them to combat problems of nonlinearity and long term drift. Several key technologies are likely to play a major role in the sensors of the future. Microelectromechanical (MEM) sensors have tremendous potential as smart sensors. Fiber optics based sensors are also emerging as a viable and competitive technology. While many types of stand alone sensors are available, only some of them can be considered for integration with smart structures. Among these, fiber optic sensors are in the forefront in their choice for incorporation into materials and structures made of carbon and glass fiber reinforced polymer composites.
The advantages of fiber optic sensors (FOS) include freedom from EMI, wide bandwidth, compactness, geometric versatility and economy. In general, FOS is characterized by high sensitivity when compared to other types of sensors. FOS is also passive in nature due to the dielectric construction. Many signal processing devices (e.g., splitters, combiners, multiplexers, filters, delay lines) can also be made of fiber elements, thus enabling the realization of an all-fiber measuring system. Recently, photonic circuits (Integrated Optics) has been proposed as a single chip optical device or signal processing element which enables miniaturization, batch production, economy and enhanced capabilities.
A fiber optic sensor in general consists of a source of light, a length of sensing (and transmission) fiber, a photodetector, demodulation, processing and display optics and the required electronics. Interferometric (phase) sensors are based on the detection of changes in the phase of light emerging out of a single mode fiber. Interferometric fiber optic sensors are by far the most commonly used sensors since they offer the best performance.
FIG. 1 shows a prior art Sagnac interferometer 100. Inside the interferometer, two counter propagating beams (one clockwise, CW, and another counterclockwise, CCW) arising from the same source, propagate along the same closed waveguide path 110. The CW and CCW beams are recombined in a quadrature coupler 140, where interference takes place. Data signals are thus selectively outputted from data output 125, depending upon the type of interference that occurs in quadrature coupler 140. The use of a terahertz optical asymmetric demultiplexer (TOAD) is based upon the concepts of a Sagnac interferometer. The TOAD has ultra-fast switching capabilities and is used to demultiplex an incoming data stream. All-optical digital bits are read for further signal processing or routing onto a particular path of an all-optical communication network. Prior art Sagnac loops have a single control port 115 for injecting the control signal via a coupler 130, typically made of fiber optic material. The control signal is used to control the state of a nonlinear element (NLE) 105 inserted in the waveguide path 110. The NLE is often a semiconductor optical amplifier (SOA). Data is inputted via an input data port 120 and outputted via an output port 125. The control signal is eliminated at the output by inserting a polarization or wavelength filter 135.
One deficiency with prior art TOADs is that the physical size of the coupler 130 and the material used to make the coupler 130 makes such TOADs unsuitable for monolithic fabrication. Accordingly, there is an unmet need for a monolithically integrated TOAD to keep size down to a minimum without affecting performance.
Another deficiency with prior art TOADs is that they do not provide a smooth transition for signals to be inputted into and outputted from an integrated structure. Accordingly, there is an unmet need for monolithically integrating the structures of the TOAD so as to ease the device to fiber alignment and thus enhance the coupling efficiency of light into and out of the device.
Yet another deficiency with prior art TOADs is that all or part of the control signal is outputted along with the switched (demultiplexed) data signal, thus requiring filtering and/or complicated processing techniques at or past the output. Accordingly, there is an unmet need for a TOAD wherein inputted control signals are removed once they pass through the nonlinear device inserted in the waveguide loop, but before the control signals reach the data output of the TOAD.
The present invention provides for the use of a ring resonator as a coupler to provide a separate input and output for a clocking control signal. The control signal is coupled into and out of the optical device without perturbing its geometry. By providing independent input and output ports for the control signal, filtering and/or other complicated processing techniques at the output of the device can be avoided.
The present invention also provides for the monolithic integration of a variety of optical device structures, which together will produce superior performance and increased utility over the prior art. In the present invention, asymmetric twin waveguide structures are integrated at all transitions to the xe2x80x9coutside worldxe2x80x9d such as connections to external fiber or other optical waveguide components.
Another embodiment of the present invention also provides the addition of a ring resonator as a coupler to route the data signal from the device once it is switched from a first path to a second path.